Portable scanning spectrophotometer

ABSTRACT

The specification discloses a portable spectrophotometer ( 10 ) providing improved movement and control of the sample (S) during analysis. The unit ( 10 ) includes a base ( 12 ) and an upper assembly ( 14 ) supported on the base ( 12 ) for floating movement. Both a spectral measurement engine ( 20 ) and drive rollers ( 104 ) are contained within the upper assembly. The base ( 12 ) includes independently suspended idler rollers ( 16 ), and the drive rollers ( 104 ) engage the idler wheels ( 16 ), so that at least a portion of the weight of the upper assembly ( 14 ) is borne by the engaging drive rollers ( 104 ) and idler rollers ( 16 ). The upper assembly ( 14 ) therefore floats up and down with samples (S) of varying thickness moving between the rollers ( 104  and  16 ). Additional upstream idler rollers ( 18  and  24 ) on the base and the upper assembly engage one another and bear a portion of the weight of the upper assembly ( 14 ) to create tension in opposition to the drive rollers ( 104 ) to hold the sample (S) taut. A planar media guide ( 130 ) is located on the underside of the upper assembly ( 14 ) and surrounds the spectral engine ( 20 ) to engage the sample (S) and reduce flexing and bowing of the sample (S). A manually actuated backer ( 30 ) is supported by the base ( 12 ) to selectively present to the spectral engine ( 20 ) one of two areas ( 52   a  and  52   b ) with different reflective properties. The unit ( 10 ) may include a first light source ( 21 ) in the spectral engine and a second light source ( 60 ) in the backer ( 30 ) so that the spectrophotometer ( 10 ) is capable of both reflective and transmissive analysis.

This is a continuation of application Ser. No. 09/704,005, filed Nov. 1,2000 (U.S. Pat. No. 6,285,452), which is a continuation of applicationSer. No. 09/341,156, filed Jul. 2, 1999 (now U.S. Pat. No. 6,198,536)which is a 371 of PCT/US98/18108 filed Sep. 1, 1998.

TECHNICAL FIELD

The present invention relates to color measurement instruments, and moreparticularly, to spectrophotometers.

BACKGROUND ART

Color measurement instruments for many and varied applications are wellknown. These instruments are used, for example, to determine colorconsistency in printed material, photographic material, textiles, andplastics. The most comprehensive color measurements are obtained byinstruments known as spectrophotometers, which measure the spectraldistribution of light and give a percentage reflection or transmissionat many segments in the visible color spectrum.

The field of desk top publishing has expanded greatly in recent years,and color output devices such as color printers, plotters, proofers havebecome widely used. The color output devices are often controlled bycomputer software, which transmits control signals to the printerdefining color to be produced. To assure color quality, it is desirableto be able to calibrate color printers to produce a selected quality ofcolor for printed material produced by a number of different printers.Additionally, data defining a color product may be transmitted to remotelocations to be printed by a variety of printers. In order to be able toprovide a product of consistent color characteristics, a comparison to acolor standard is required. All of these functions require the accuratemeasurement of many samples of different colors produced on the device.These colors are produced using only a few colorants—usually cyan (C),magenta (M), yellow (Y), and black (K).

A color measurement instrument, such as a spectrophotometer, includes acolor measurement engine having an optical pick-up. Additionally, manyinstruments include a drive mechanism for moving either the sample orthe engine to effect relative movement between the two. The registrationof the sample with respect to the engine and the controlled movement ofthe sample or the engine are critical components in obtaining consistentand accurate measurements. Only small changes in the distance betweenthe sample and the measurement engine can create significant errors andinconsistencies in the color measurement.

Prior color measurement instruments are illustrated in U.S. Pat. No.5,369,494 issued Nov. 29, 1994 and entitled “Portable ScanningColorimeter”; U.S. Pat. No. 5,118,183 issued Jun. 2, 1992 and entitled“Automated Strip Reader Densitometer”; and U.S. Pat. No. 5,062,714issued Nov. 5, 1991 and entitled “Apparatus and Method for PatternRecognition.” In these units, the sample drive mechanism is located inthe base, while the color measurement engine is located in an assemblyabove the base. Because these two primary components are located indifferent housings, there is the possibility that sample registrationand movement is not as precisely controlled as required for present daymeasurement. Accordingly, artisans continue to seek improved structuresfor maintaining improved consistency and accuracy in sample registrationand movement.

DISCLOSURE OF INVENTION

The aforementioned issues are addressed in the present inventionproviding improved sample registration and movement within a portablespectrophotometer. The instrument contains a mechanical drive systemthat transports the sample past the measurement engine in a precisefashion.

First, the spectrophotometer includes a base and an upper assemblysupported for floating movement on the base. Both the color measurementengine and the sample drive mechanism are located within the upperassembly. As the sample is drawn between the base and the upperassembly, the upper assembly can float with samples of various andvarying thickness. This approach reduces or even eliminates the need forseparate tensioning devices within the drive system, such as springsand/or close tolerances.

Second, the drive mechanism includes a plurality of drive wheels, andthe base includes a plurality of independently suspended idler rollers,each of which engages and supports one of the drive wheels. Theindependently suspended rollers flex to accommodate samples of varyingand various thicknesses.

In a third embodiment of the invention, the drive rollers are located“downstream” (in the direction of sample travel) from the colormeasurement engine. Tension rollers are provided upstream of the colormeasurement engine to at least partially resist movement of the samplein response to the drive rollers. The tension created within the sampleimproves its consistent maintenance in a uniform plane and therefore itsconsistent registration with the color measurement engine.

In a fourth embodiment of the invention, a planar, low-friction mediaguide is located on the underside of the upper assembly to engage thetop surface of the sample. The thickness of the media is approximatelythe same as the distance that the drive wheels extend from the upperassembly, so that the media guide consistently engages the top surfaceof the sample. Therefore, the media guide improves the registration ofthe sample with respect to the color measurement engine; and the mediaguide assists the upper assembly in riding the top surface of thesample.

In a fifth embodiment, a two-position backer is provided in the base.The backer includes two separate areas with different reflectiveproperties. The backer is readily manually movable so that either of thetwo areas can be aligned with the optical pickup of the colormeasurement engine. For example, the two areas may be white lightdiffusing opal and stable uniform black. In an alternative embodiment,the light diffusing opal may be illuminated for transmissive analysis.

In a sixth aspect of the invention, the spectrophotometer is capable ofboth reflective and transmissive analysis. A first light source isincluded within the color measurement engine and is activated only whenreflective analysis is desired. A second light source is included withinthe base, is aligned with the color measurement engine, and is activatedonly when transmissive analysis is desired.

These and other objects, advantages, and features of the invention willbe more readily understood and appreciated by reference to thedescription and the drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a right front perspective view of the spectrophotometer of thepresent invention;

FIG. 2 is a left front perspective view of the spectrophotometer;

FIG. 3 is a perspective view of the spectrophotometer with the basecomponents exploded;

FIG. 4 is a perspective view of the base;

FIG. 5 is a top plan view of the base showing the backer in a firstposition;

FIG. 6 is a top plan view of the base showing the backer in its secondposition;

FIG. 7 is a bottom plan view of the base showing the backer in thesecond position;

FIG. 8 is a sectional view taken along line VIII—VIII in FIG. 5;

FIG. 9 is a perspective view of the underside of the base with analternative backer capable of illumination;

FIG. 10 is a perspective exploded view of the upper assembly;

FIG. 11 is a front elevation view of the drive shaft and motor;

FIG. 12 is an enlarged perspective view of the drive shaft bearing;

FIG. 13 is a fragmentary bottom plan view of the upper assembly showingthe media guide; and

FIG. 14 is a sectional view of the spectrophotometer taken along theline XIV—XIV in FIGS. 1 and 2.

MODE FOR CARRYING OUT THE INVENTION

A spectrophotometer constructed in accordance with a preferredembodiment of the present invention is illustrated in the drawings andgenerally designated 10. As perhaps best illustrated in FIGS. 3 and 10,the spectrophotometer includes a base 12 and an upper assembly 14supported on the base. The base includes two sets 16 and 18 of idlerrollers. The upper assembly 14 includes a spectral analysis engine 20, adrive assembly 22, and tension rollers 24. The engine 20 includes anoptical pick-up 75. The drive rollers 22 of the upper assembly engagethe idler rollers 16 of the base, and the tension rollers 24 of theupper assembly engage the idler rollers 18 of the base all to partiallysupport the upper assembly 14 on the base 12. The drive rollers 22 pullor draw the sample S (see FIG. 1) through the spectrophotometer 10 andpast the optical pick-up 75. The tension rollers 24 create a tension onthe sample S to maintain the sample in a consistent plane.

I. Base

The base is perhaps best illustrated in FIGS. 3-8. Generally, the base12 includes a body 26, idler rollers 16 and 18, and a backer 30.

The body 26 is plastic and includes a connector portion 32 and a sampleportion 34. The connector portion 32 includes a platform 36, a pair ofalignment pins 35 a and 35 b, and a pair of integrally molded springclips 38. The platform 36 provides an engagement surface for the upperassembly 14. The pins 35 a and 35 b interfit with apertures 97 a and 97b (see FIG. 10) respectively to prevent relative rotation of the upperassembly 14 on the base 12 in a horizontal plane. The spring clips 38include catches 39 (see FIG. 4) above the platform 36 and actuatingportions 40 (see FIGS. 7 and 9) that extend through and below theplatform. The actuating portions may be manually actuated from theunderside of the base 12 to release the upper assembly 14 from the base12.

The sample portion 34 of the base 12 is generally planar and supportsthe idler rollers 16 and 18 and the backer assembly 30. The forward edge41 of the platform is rounded to facilitate insertion of the sample Sbetween the base 12 and the upper assembly 14. A 35 mm groove or guide43 in the forward edge 41 facilitates insertion and alignment of a stripof 35 mm film (not shown). A race-track shaped window 39 is defined in acentral portion of the sample portion 34.

The body base includes integral fingers 47 a, 47 b, and 47 c on itsunderside. The finger 47 a is opposed to the fingers 47 b and 47 c, andthe fingers slidingly receive the backer assembly 30 as will bedescribed. A foot 45 is mounted at each of the four corners of the basebody. Preferably, the feet are fabricated of a relatively high-frictionmaterial to assist in securely support the unit 10 on a smooth surface.

All of the idler rollers 16 and 18 are generally identical to oneanother. In the preferred embodiment, each is fabricated on plastic. Asseen in FIG. 3, each includes a roller body 16 a or 18 a and a pair ofstub shafts 16 b or 18 b extending therefrom.

Each of the rollers 16 is supported by a suspension arm 40. Each of thesuspension arms 40 terminates in a bearing portion 42 which receives thestub shafts 16 b and rotatably supports the associated roller 16. Eachof the suspension arms 40 is integral with the remainder of the basebody 26. The base 26 is fabricated of a resiliently flexible plastic,and therefore each of the arms 40 is resiliently deflectable downwardlyunder the weight of the upper assembly 14.

Similarly, each of the idler rollers 18 is supported for independentsuspension on a suspension arm 44. Each of the suspension armsterminates in a bearing portion 46 for which receives the stub shafts 18b and rotatably supports the associated roller 18. As with arms 40,suspension arms 44 are resiliently deflectable in the downward directionunder the weight of the upper assembly 14. When not deflected, therollers 16 and 18 lie within and define a plane. The rollers 16 and 17are retained in the bearing portions 42 and 46 because the stub shafts16 b and 18 b extend under the sample portion 34. Any of the rollers 16and 17 can be removed by pressing the supporting arm downwardly andlifting the roller from the bearing portion.

The backer assembly 30 is illustrated in FIGS. 3 and 7-8 and includes abody 49, a spring plunger 50, and an opal glass 51. The body 49 is heldbetween fingers 47 a on one side and 47 b and 47 c on the other side forsliding movement. The spring plunger 50 cooperates with detents (notvisible) in the underside of the base body 26 to releasably catch theassembly in either of two opposite positions. The backer body 49includes a recessed area 54 that facilitates removal of the backerassembly 30 from the base body 26 when the recessed area 54 is alignedwith the finger 47 a.

The body 49 includes a platform portion 52 extending upwardly from theremainder of the body 49 and into the window 39 of the base body 26. Theplatform provides two separate areas with different reflectiveproperties. The first area 52 a is stable uniform black. The second area52 b supports the white light diffusing opal glass 51. The white opalglass 51 is secured in position on the platform 52 using a solventadhesive or other suitable interconnection means.

An alternative backer assembly 30′ is illustrated in FIG. 9. Thealternative backer assembly 30′ is capable of providing illumination foroperation of the spectrophotometer 10 in a transmissive mode ofanalysis. In the alternative backer 30′, an illumination source 60 ispositioned within the cavity 37 directly below the opal glass 51 (seeFIG. 8). A power cord 62 extends from the backer assembly 30′ andterminates in a plug 64 mounted within the backer base 26. The cord 62is secured under wire management fingers 66, which are integral with thebase body 26. The plug or connector 64 is held in position by the basebody 26 for automatic connection with the upper assembly 14 when theupper assembly 14 is installed on the base 12.

II. Upper Assembly

The upper assembly 14 is illustrated in FIGS. 10-14. The upper assembly10 includes a housing 70, a spectral measurement engine 20, a driveassembly 22, and a lower plate 72.

The housing 70 is injection molded of plastic to house the remainingupper assembly components. The housing includes an integral alignmentmark 71 centered above the film strip guide 43 and linearly aligned withthe spectral engine 20 to assist a user with properly aligning thesample S for scaring by the engine.

The spectral measurement engine 20 of the preferred embodiment isgenerally well known to those skilled in the art. For example, onesuitable spectral engine is illustrated co-pending application Ser. No.08/714,969 filed Sep. 17, 1996 by Berg et al and entitled “CompactSpectrophotometer,” now U.S. Pat. No. 6,002,488, the disclosure of whichis incorporated by reference. Other measurement engines, such as thosefor colorimeters and densitometers, can be used depending on theapplication. Generally speaking, the engine 20 includes an opticsassembly 74, a printed circuit board (PCB) assembly 76, and a controlboard shield 78. The optics assembly 74 includes an optical pick-up 75(see FIG. 14). The PCB assembly 76 and the shield 78 are secured to theoptics assembly 74 using screws 80 and star lock washers 82. The opticsassembly 74 is secured to the aluminum stand-offs on the bottom plate 72using screws 81 and star lock washers 83. Additionally, the bottom plate72 is secured to the optics assembly 74 using screws 85. The aluminumbottom plate 72 and the aluminum stand-offs 98 dissipate heat generatedby the optics assembly and most notably by the illuminators 77. A wiretie 87 is included for wire management.

A plurality of illuminators 77 (see FIG. 14) are included within thespectral engine 20 to illuminate the sample S when the unit 10 isoperated in the reflective analysis mode. The illuminators 77 areactuated only in the reflective mode (i.e. not in the transmissivemode).

The bottom plate 72 is generally planar, is fabricated of aluminum andprovides an underside to the upper assembly 14. The perimeter of thebottom plate 72 is dimensioned to closely fit within the bottom of thehousing 70. The plate 72 is secured to the housing 70 using screws 73.

The plate define two rectangular apertures 96 that receive the lockingarms 38 of the base 12. When the upper assembly 14 is attached to thebase 12, the catches 39 of the locking arms 38 engage the upper surfaceof the bottom plate to lock the upper assembly on the base; and thebottom plate 72 rests upon the platform 36 of the base 12 to at leastpartially support the weight of the upper assembly. The plate furtherdefines two alignment apertures 97 a and 97 b that receive the alignmentpins 35 a and 35 b respectively of the base 12. The interfit of thelocking arms 38 within the apertures 96 and the interfit of thealignment pins 35 within the apertures 97 prevents the upper assemblyfrom rotating in a generally horizontal plane, but permits the upperassembly to float or pivot in a generally vertical plane.

The plate 72 defines a series of elongated apertures 90 through whichdrive rollers extend, a pair of elongated apertures 92 through whichidler rollers extend, and an optics aperture 94 aligned with the opticalpick-up 75 (see FIG. 14).

The drive assembly 22 (see FIGS. 10-11) includes a drive shaft assembly100 and a motor assembly 102. The drive shaft is secured to the motorassembly using set screws 103. The drive shaft assembly 100 includesfive drive wheels 104 of uniform diameter with the wheels being evenlyspaced from one another. Because the upper assembly is free to float ina vertical plane, the drive shaft assembly is also free to float in avertical plane. The individual suspension of the idler rollers 16 underthe drive rollers 104 accommodates such angular floatation.

Each of the wheels 104 defines a circumferential groove 106 (see FIG.11). An O-ring 108, which acts as a tire, is fitted within each of thegrooves 106. Each of the O-rings is fabricated of a relativelyhigh-friction material for gripping the sample to be analyzed. Thematerial of the preferred embodiment is precision silicone. The motorassembly 102 is generally well known in the art. The motor of thepreferred embodiment is a high-torque gear motor or a stepper motor. Thedrive rollers 104 extend through apertures 90 to extend approximately0.3 millimeter (mm) from the lower surface of the bottom plate 72 (seeFIG. 14). As currently implemented, the drive assembly moves or pullsthe sample S at a speed of approximately 3 centimeters (cm) per second.

The drive assembly 22 is secured to the bottom plate 72 by the drivebearings 110 illustrated in greatest detail in FIG. 12. Each of thedrive bearings 110 is generally U-shaped, defining an interior having acircular portion 112 and a pair of opposed flat portions 114. Thedistance between the flat portions 114 is less than the diameter of thecircular portion 112. The drive bearings 110 are fabricated ofbearing-quality plastic or other resiliently deformable material.Accordingly, the legs can be spread slightly to fit the bearing over thedrive shaft 100. The drive shaft then clicks into the circular portion112. Screws 116 (FIG. 10) are inserted through holes 118 in the bearing110 to lock the drive shaft within the circular portion 112 and tosecure the bearing to the bottom plate 72. Lubricant preferably isincluded within the bearing 110 to facilitate rotation of the driveshaft 100.

Idler rollers 24 (see FIG. 10) are rotatably supported on the bottomplate 72 by way of bearings 120 and screws 122. The idler rollers 24extend through apertures 92 to extend approximately 0.3 millimeter (mm)from the lower surface of the bottom plate 72 (see FIG. 14).

The media guide 130 is illustrated in FIGS. 3 and 13-14 and is agenerally planar piece of relatively low-friction material. Thepreferred material of the present embodiment is a bearing-qualitymaterial that is soft enough to avoid damage of the sample S. Ascurrently implemented, the material is a high-density polypropylene. Asviewed in FIG. 3, the media guide is milk-can shaped having a relativelynarrow forward portion 132 to fit between the idler rollers 24. Therearward portion 134 defines a central aperture 136 aligned with theoptics aperture 94 in the base plate 72 and with the optical pick-up 75of the color measurement engine 20. The media guide 130 is adhered tothe bottom plate 72 using a pressure-sensitive adhesive or othersuitable attachment means. The thickness of the media guide isapproximately 0.3 mm so that it projects from the lower plate 72approximately the same distance that the idler rollers 24 and the driverollers 104 project from the lower plate 72. Consequently, the rollers24 and 104 and the media guide 130 all lie within and define a plane.

As seen in FIG. 1, the upper assembly further includes a 12-volt powerconnection 132 for powering the unit 10, an RS-232 port 134 for serialcommunication with a personal computer (PC) or other digital device, anda push-button 136 for actuating and operating the unit.

III. Operation

The operation of the spectrophotometer 10 is perhaps best illustrated inFIGS. 1 and 14. For purposes of reference, the area above the backerassembly 30 and below the optical pick-up 75 is referred to as thescanning station 140. The backer assembly 30 is aligned with the opticalpick-up across the scanning station.

If necessary, the reflectance of the backer assembly 30 is selected bymanually sliding the backer assembly to either of its two selectablepositions. In the first position, the stable uniform black portion 52 aof the platform 52 is presented to the color measurement engine 20. Inthe second position, the white light diffusing opal glass 51 in portion52 b is presented to the engine 20.

A sample S (FIG. 1), having color patches S′, to be analyzed is alignedwith the alignment mark 71 on the upper assembly and fed or pushedbetween the base 12 and the upper assembly 14. The leading edge of thesample S passes between the tension rollers 24 on the upper assembly andthe idler rollers 18 on the base. The sample continues through thescanning station 140 until the forward edge of the sample S is grippedby the drive wheels 104, whereupon the sample is pulled between thedrive rollers and the associated idler rollers 16. Spectral analysis orother color measurement operations are conducted on the sample S as itis drawn past the color measurement engine 20 and specifically theoptical pickup 75.

As the sample moves between the idler rollers 18 and 24, the suspensionarms 44 flex to permit the individual rollers 18 to move downwardly.Similarly, as the sample is drawn between the drive rollers 104 and theidler rollers 16, the individual suspension arms 40 flex to permit therollers 16 to move downwardly. Also, the tension rollers 24 and thedrive rollers 108 engage and ride along the top surface of the sample Sto assist in registration of the sample with respect to the opticalpick-up 75. The free floating ability of the upper assembly 14 and theindividual suspension of the idler rollers 18 facilitate the accuratecolor measurement of samples of varying thickness. The upper assembly 14rides along the top surface of the sample S to maintain a desiredphysical registration or relationship between the top surface of thesample and the engine 20.

As noted above, the tension rollers 24, the drive rollers 104, and themedia guide 130 all project a substantially equal distance from thebottom plate 72. Accordingly, the media guide 130 also engages the topsurface of the sample S to further assist in registration. The mediaguide 130 prevents flexing or bowing of the sample within the scanningstation as may occur, for example, if the trailing edge of the sample isdropped below or is lifted above the level of the scanning station 140.

The spectrophotometer may be operated in either the reflective or thetransmissive mode. When operated in the reflective mode, only theilluminators 77 are actuated so that the top surface of the sample S isilluminated in accordance with the ANSI standard 45°/0° reflectionmeasurement. When operated in the transmissive mode, only the baseilluminator 60 within the backer assembly 30 is actuated to illuminatethe sample from beneath in accordance with the ANSI standard 180°/0°transmissive measurement.

The above descriptions are those of preferred embodiments of theinvention. Various alterations and changes can be made without departingfrom the spirit and broader aspects of the invention as defined in theappended claims, including the Doctrine of Equivalents.

What is claimed is:
 1. A reflective color measurement instrumentcomprising: a color measurement station; a color measurement engineincluding an optical pick-up directed toward said station; and a backerin said station and having first and second portions with differentreflective properties, said first portion comprising whitelight-diffusing opal, said second portion comprising stable uniformblack, said backer being manually movable between first and secondpositions wherein only one of said first and second portionsrespectively is aligned with said optical pick-up, whereby a user canmanually select which of the reflective properties is to be presented tosaid optical pick-up by said backer.
 2. A color measurement instrumentas defined in claim 1 wherein said backer is slidable.
 3. A colormeasurement instrument as defined in claim 1 wherein said colormeasurement instrument comprises a spectrophotometer.
 4. A colormeasurement instrument for measuring one or more colors on a flat samplewithout bending the sample during measuring, said instrument comprising:a sample area; a color measurement engine including an optical pick-upaligned with said sample area; pulling means for engaging the sample andfor pulling the sample through said sample area past said opticalpick-up in a linear direction so that said optical pick-up scans a firstlinear portion of the sample, said pulling means engaging the sampleonly in one or more second portions mutually distinct from the firstlinear portion, whereby said pulling means does not engage the firstlinear portion of the sample; tensioning means for engaging the sampleand for resisting movement of the sample in the linear direction as thesample is pulled through said sample area, said tensioning meansengaging the sample only in one or more third portions mutually distinctfrom the first linear portion, whereby said tensioning means does notengage the linear portion of the sample; and said sample area, saidpulling means, and said tensioning means being arranged so that thesample remains flat when entering, moving through, and exiting saidinstrument.
 5. A color measurement instrument as defined in claim 4wherein said tension means is located upstream of said optical pick-up.6. A color measurement instrument as defined in claim 4 wherein saidtension means comprises a plurality of pairs of pinch rollers betweenwhich the sample passes.
 7. A color measurement instrument as defined inclaim 6 wherein at least one of said rollers in each pair isindependently resiliently supported to enable the distance between therollers to vary to accommodate samples of varying thickness.
 8. A colormeasurement instrument as defined in claim 4 wherein said colormeasurement instrument comprises a spectrophotometer.